Since a plastic lens is lightweight and hardly broken as compared to an inorganic lens, and can be tinted, in late years, it has quickly come into wide use as an optical component of a spectacle lens, a camera lens and the like.
A spectacle lens has been required to have many functions such as (3) excellent heat resistance, (4) easy tintability, (5) resin strength capable of enduring processing and the like in addition to optical performance such as (1) high refractive index, (2) high Abbe's number. Various resin materials for lenses have hitherto been developed and used accordingly.
Of such materials, a polythiourethane resin has been developed as a representative example (refer to Patent Documents 1 and 2).
Furthermore, a polythiourethane resin using an isocyanate compound having a specific chemical structure is excellent in high refractive index, high Abbe's number, high heat resistance and impact resistance, and made into a plastic lens which is highly excellent in the balance thereof (refer to Patent Document 3).
On the other hand, in recent years, fashionability has been demanded in a spectacle lens so that a tinted lens has been increasingly demanded. When tintability is said to be good, the tinting temperature can be lowered and a load on a spectacle lens can be reduced. However, since tintability and heat resistance of a base material are in a tradeoff relationship, a lens having heat resistance without having any problem in practical use and excellent in tintability has been in demand. Furthermore, since fashionability is further pursued, a resin has been subjected to various processings. However, when resin strength is not sufficient, the resin might be broken upon processing or the yield rate becomes worsened. For that reason, resin strength has been demanded to be further improved.
As described above, a plastic lens has been exemplified, but in a polythiourethane resin, tintability and resin strength have been demanded to be improved.
Patent Document 1: Japanese Patent Laid-open No. 1990-270859
Patent Document 2: Japanese Patent Laid-open No. 1995-252207
Patent Document 3: Japanese Patent Laid-open No. 1991-124722